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# The rate of a reaction increases with concentration.

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Introduction

Jon Leary 11SA Rates of Reactions - Coursework Hypothesis The rate of a reaction increases with concentration. Prediction I predict that when the concentration of the acid is raised, the rate of the reaction will increase. This is because, when the concentration of acid is higher, more acid particles are present in a given volume of the solution, therefore, more acid particles are available to collide with magnesium particles. This consequently increases the chances of successful collisions (those resulting in a reaction) occurring. As the collision theory states, the more collisions that occur in a period of time, the faster the rate of the reaction. This is because the reaction only occurs when acid and magnesium particles collide and successfully join together to form magnesium chloride and hydrogen particles. In a previous experiment with acid and marble chips, I found that higher concentrations of acid increased the rate of reaction quite significantly. About the Reaction The reaction that we are using to prove the above hypothesis is between an acid and a metal. An acid and a metal will produce a salt and hydrogen when reacted together. Since we are trying to measure the rate of a reaction, a reaction that produces a non-toxic gas is the most suitable as it is easy to see when a given quantity of gas has been produced. The reaction is recorded as beginning when the gas is first produced and stopping when it is no longer produced. ...read more.

Middle

I then decided to test how long it would take to produce 20cm� of hydrogen with 0.4M hydrochloric acid, as this is the lowest concentration of acid molecules that will be used in the main experiment, so would take the most time. I found that it took 407s, a time which is highly impractical when three or more must be done in a lesson and similar time taken for slightly higher concentrations. I then tried 5cm of magnesium at this concentration and found that it produced 20cm� of hydrogen in 181s - a much more practical length of time. After the second set of results, I decided to use 5cm of magnesium in the main experiment, as it was not too slow, always produced enough gas and was not to quick to accurately record. I will use 50cm� of solution, as previously stated. Method 1. Measure out 50ml of 2M hydrochloric acid solution in a measuring cylinder and pipette for accuracy and pour into a small conical flask. 2. Cut a 5cm strip of magnesium ribbon using a ruler and clean with emery cloth to remove any dirt that would reduce the surface area and consequently the rate of reaction (see key variables section). 3. Fill the measuring cylinder with water and place upside-down in the water trough. 4. Insert the delivery tube into the measuring cylinder, so that all gas travelling through the delivery tube flows into the measuring cylinder. ...read more.

Conclusion

and drying of the conical flasks before reuse. The more major inaccuracies could have been caused by different concentrations of the acid before it was mixed with the water (I got my acid from many different bottles) or possibly the fact that the magnesium floated on the surface, exposing only half of its total surface area to the acid. These problems could be rectified by only getting acid from one bottle and making sure the magnesium either sinks or floats on the surface for all the reactions to ensure continuity (otherwise, the surface area variable will have been altered - sinking would expose more particles to the acid and floating less). To reduce the effect of the exothermic reaction on the reaction as a whole, the conical flask could be placed in a water bath to help maintain a constant temperature. I could also investigate the effect of temperature separately using different temperature water baths and ice. There is currently no known catalyst for the reaction between magnesium and hydrochloric acid, but the magnesium could be cut up into smaller pieces to increase its surface area. I had to adapt the method after the first few tries, because I had been putting the magnesium in the conical flask before the acid and consequently, hydrogen began to be produced before the bung could be secured. I changed the method to put the acid in first, then just drop the magnesium into it as this is quicker and allows the bung to be secured before any hydrogen can escape. ...read more.

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